Ignition coils

ABSTRACT

An ignition coil has a secondary winding wound on a coil and a primary winding which is co-axial with the secondary winding and is spaced therefrom by a layer of corrugated electrically insulating material defining a plurality of channels extending parallel to the axis of the core. At least one layer of the primary winding is wound on the secondary winding between the secondary winding and the layer of corrugated electrically insulating material.

United States Patent 11 1 Hillyard 1451 Feb. 13, 1973 [541 IGNITIONCOILS 2,701,345 2/1955 Henry 336/60X 3, 02,149 1 1967 F 11 ....336 60X[75] Inventor: g T Hillyard, 30mm, 2,316,148 2/1947 32:21:11 et a1..336/60 x ng an FORElGN PATENTS OR APPLlCATlONS [73] Assignee: JosephLucas Industries Limited,

Birmingham, England 199,118 1923 Great Britain ..336/60 [22] Filed: Nov.23, 1971 Primary Examiner-Thomas J. Kozma AttorneyHolman & Stern {21]Appl. No.: 201,466 1 [57] ABSTRACT [30] Foreign Application PriorityData An ignition coil has a secondary winding wound on a Nov. 28, 1970Great Britain ..56,647/70 and a p whlch the secondary wmdlng and 1sspaced therefrom by a layer of corrugated electrically insulatingmaterial defining if 23 a plurality of channels extending parallel tothe axis of 1 l H01 5/14 the core. At least one layer of the primarywinding is [58} Field of Search ..336/55, 60, 58, 185, 69, 70 wound onthe secondary winding between the Secon dary winding and the layer ofcorrugated electrically [56] References C'ted insulating material.

3,170,134 2/1965 Palmer ..336/6O X 3,237,136 2/1966 Ford .....336/60 X3,071,845 1/1963 Leonard et al. ..336/60 X a c 1 I 11:22:

IGNITION COILS This invention relates to ignition coils for use in sparkignition systems for road vehicles.

An ignition coil according to the invention includes a secondary windingwound on a core, and a primary winding which is co-axial with thesecondary winding, the primary winding being spaced from the secondarywinding by a layer of corrugated electrically insulating materialdefining a plurality of channels extending parallel to the axis of thecore, characterized in that at least one layer of the primary winding iswound on the secondary winding between the secondary winding and thelayer of corrugated electrically insulating material.

An example of the invention is illustrated in the accompanying drawings,in which:

FIG. 1 is a longitudinal section through an ignition coil, and

FIG. 2 is a section on the line 22 in FIG. 1.

Referring to the drawings, the coil includes a generally cylindricalmetal casing having an integral base at one end, and closed at the otherend by a moulded insulating cap 11. The cap 11 carries the low tensionterminals 12, 13 and high tension terminal 14 of the ignition'coil, andextending axially within the casing between the cap 11 and an insulatingsupport 15 engaged with the base of the casing is a laminated iron core16. Surrounding the core is a cylindrical, cardboard or similarelectrically insulating former l7, and wound on the former is thesecondary winding 18 of the ignition coil. The wire constituting thesecondary winding 18 is coated with a varnish so that adjacentconvolutions of the winding are insulated from one another, and adjacentlayers of the secondary winding 18 are in addition insulated from oneanother by intermediate layers of insulating paper.

Surrounding the secondary winding is one layer 20 of the primarywindingZl of the coil. The wire of the primary winding is provided witha coating of insulating varnish, and the layer 20 is further insulatedfrom the secondary winding 18 by means of several insulating paperlayers (not shown). Surrounding the layer 20 is a cylindricalelectricallyinsulating single layer 19 formed from corrugated paperwrapped around the layer 20, the corrugations of the layer 19 extendingparallel to the core 16. A suitable paper is the flexible paper soldunder the trade name Carbion". Wound on the corrugated layer 19 is theremainder of the primary winding 21 of the coil, and as in the case ofthe secondary winding, adjacent layers of the primary winding areinsulated from one another not only by the varnish, but also byintermediate layers of insulating paper. An additional layer (not'shown)of paper is provided to insulate the winding 21 from an iron shield 22lining the casing 10. The winding 21 is of course continuous and extendsthrough the layer 19.

i The primary winding 20, 21 is formed'from a relatively few turns ofrelatively thick wire, while the secondary winding 18 is formed from arelatively large number of turns of relatively thin wire. The wire ofthe primary winding is sufficiently thick to enable connections to bemade thereto quite easily, but the wire of the secondary winding is toothin to permit connections to be made satisfactorily, and so the ends ofthe secondary winding are electrically connected during manufacture ofthe windings to a pair of conductive braids. The end of the primarywindingdefined by the layer 20 and the one endof the secondary winding18 are electrically interconnected and are connected to the terminal 12.The other end of the secondary winding is electrically connected to theterminal 14 through the core 16 of the coil, and a spring 23 which alsolocates the core in position. The other end of the primary winding iselectrically connected to the terminal 13. The terminal 12 is connectedin use through the contact breaker of an ignition system to earth, theterminal 14 is connected to the rotor arm of an ignition distributor ofthe system,

I and the terminal 13 is connected to one terminal of the battery, theother terminal of which is earthed. The free volume in the casing isfilled with oil which acts as a coolant for the coil. it will of coursebe appreciated that the two parts 20, 21 of the primary winding areinterconnected through the layer 19.

it will be appreciated that since the corrugations of the layer 19between the primary and secondary windings extend axially, in adirection parallel to the core, then axially extending passages aredefined within which in use the oil filling the casing can circulate. Inthis way, the windings of the coil are more efficiently cooled thanthose of a comparable ignition coil formed without the corrugated layer19. Moreover, the.corrugated layer 19 spaces the main part of theprimary winding from the secondary winding and thereby ensures that themagnetic coupling between the primary and secondary windings is looserthan the coupling between the primary and secondary windings in acomparable coil formed without the corrugated layer 19. The loosermagnetic coupling between the windings gives rise to a decrease in thetime taken for the voltage in the secondary winding to reach its peakvalue as compared with conventional coils,- and this means that lessenergy is dissipated in spurious resistive loads occurring between theterminal 14 and earth. Such loads can be caused, for example, bycondensation, dirt or products of combustion given off by the engine.The loose coupling reduces the risk of an inadequate spark beingproduced under such conditions, so rendering the coil more reliable thanconventional coils, particularly in cold conditions.

The reason for having at least one layer of the primary windingwound onthe secondary winding, with the remainder of the primary winding spacedfrom the secondary winding, is that it has been found that in this waydamage to the coil by voltage transients in the system is minimized. Itis believed that ina conventional coil without the layer 19, transientsare conducted from the secondary winding to the primary winding as aresult of the relatively low impedance capacitive connection within thecoil between these windings in addition to the physical low resistiveelectrical connection which exists between the windings. if the windingsare entirely separated by the layer 19, this capacitive connection isgreatly reduced, and so the transients can cause damage. By having partof the primary winding wound directly on the secondary winding, theadvantages of the sleeve 19 are retained, and there is still a lowimpedance capacitive path which minimizes the risk of damage by thetransients.

I claim:

1. A ignition coil including a hollow casing, a cap closing said casingand carrying the terminals of the secondary winding by a layer ofcorrugated electrically insulating material defining a plurality ofchannels extending parallel to the axis of the core, and meansconnecting said windings to said terminals.

1. A ignition coil including a hollow casing, a cap closing said casingand carrying the terminals of the coil, a core extending axially withinsaid casing, a secondary winding wound on said core, and a primarywinding which is co-axial with the secondary winding, the primarywinding having at least one layer wound on said secondary winding, butthe remainder of the primary winding being spaced from said one layerand the secondary winding by a layer of corrugated electricallyinsulating material defining a plurality of channels extending parallelto the axis of the core, and means connecting said windings to saidterminals.